During the past year, the Laboratory of Mycobacteria has continued the evaluation of the genetic, biochemical, and immunologic characterization of two immunoreactive Mycobacterium intracellulare antigens. MI43 - Nucleotide sequence analyses have previously indicated that the MI43 gene encodes a 27 kDa lipoprotein. Recently, we have confirmed biochemically, using detergent phase separation experiments and metabolic labeling with 3H palmitic acid that MI43 is a lipoprotein. We have also demonstrated that purified MI43 is recognized by 70% of the sera from patients with tuberculosis, 80% of sera from HIV-seronegative patients with MAC disease, and 50% of sera from AIDS patients with MAC disease. MI85 - Our nucleotide sequence analysis and expression in Escherichia coli suggest that the MI85 gene encodes a catalase-peroxidase, a bi-functional enzyme that may be critical for the intraphagosomal survival of mycobacteria. Because of the importance of MI85, we have generated a number of monoclonal antibodies which recognize epitopes on this antigen. Induction experiments using one of these antibodies have demonstrated that MI85 is induced three-fold by peroxide in vitro. In addition, we have identified the nucleotide sequences containing the MI85 catalase promoter and are currently characterizing the structure and activity of the promoter. Finally, we have cloned and are characterizing the catalase-peroxidase genes of M. tuberculosis and M. avium.